Coking ovens are fed with coal in the form of a coking charge. A coking charge mixture is commonly used for coking, i.e. the coking coal is ground to obtain a certain granulate, having specific and various sizes of granules. The different sizes of granules, when mixed, give a certain distribution or spectrum of granule sizes. This distribution of sizes decisively influence the bulk density of coking coal in a coke oven by affecting the packing of the coal granules in the oven. It has been found that an optimum of distribution in granulates may be achieved by mixing different sizes of granules.
Of even greater influence than bulk density, on the quality of the coke produced, is the composition of the coking coal used in the charge mixture. Different test methods have been developed in order to make attempts to evaluate the coking behavior of coal in advance. Important properties result from the coal's mineral structure (type of coal, from what type of veins it comes), chemical composition (analytical chemical composition, ash content, content of volatile components, bitumen content, state of oxidation), and the coal's physical and/or chemical properties (behavior during softening, swelling, shrinking, expansion and degasification).
Importance is also placed upon the caking properties of coal. Caking capability is the ability of coal, when heated in a vessel which permits the coal to expand freely in a plastic state and then heated further, to form a caked lump of coal. A coal having good caking capability yields not only caked coke but also molten coke. This defined caking capability may be measured either by a swelling index or by a caking number according to ROGA.
Coals having good caking capability may ultimately produce, due to operational conditions in the coke oven, coke of lower quality than coke produced from coal with lower caking capability. Therefore, the caking capability of coal is deemed to be important in retrospect. The coking capability of coal may be determined either by dilatometer testing to determine expansion or by ascertaining the Gray-King type of coke produced. As known in the prior art, determination made in the dilatation process comprises the measurement of the change of length of a conical briquette heated at the rate of 0.05.degree. C./second.
Finally, measurement of plasticity has a certain significance. What is understood by plasticity of coal, for the purposes to the instant patent application, is the capability of the coal to assume a plastic state between the temperatures of about 320.degree. and 550.degree. C. The usual methods of measuring plasticity involve the use of modified rotary viscosimeters. The results of such testing is not truly the viscosity of the coal in the usual physical sense, but the measurement is influenced by the apparatus used and therefore includes the internal friction of the solid, liquid and gaseous phases, as well as the degree of plasticity of all three phases. Such measurements are usually made in laboratories. The same is true for the measurement of the degasification properties, pressure of expansion and shrinkage, which are also tests for the quality of coal to be charged into a coke oven. The many and varied tests, of which only a few have been discussed above, used to determine the quality of the charging coal and to predict the coke quality indicate that until the method of the present invention, the control of the quality of coal to obtain high quality coke was only possible with the use of multiple measurements which made such determination very complex and cumbersome and an especially difficult prospect.
It is an object of the present invention to simplify the ascertaining of the quality of the charging material. It is a further object of the present invention to modify the charging material to produce a high quality coke.